Membrane electrode assembly and fuel cell using the same

ABSTRACT

A membrane electrode assembly includes a proton exchange membrane and at least one electrode. The at least one electrode includes a carbon nanotube composite structure. The carbon nanotube composite structure includes a carbon nanotube structure and a catalyst material. The carbon nanotube structure includes a plurality of carbon nanotubes and the catalyst material is dispersed on the carbon nanotubes. A fuel cell using the membrane electrode assembly is also provided.

RELATED APPLICATIONS

This application is related to co-pending applications entitled“MEMBRANE ELECTRODE ASSEMBLY AND BIOFUEL CELL USING THE SAME”, U.S.patent application Ser. No.12/384,964, filed Apr. 9, 2009; “MEMBRANEELECTRODE ASSEMBLY AND BIOFUEL CELL USING THE SAME”, U.S. patentapplication Ser. No.12/384,963, filed Apr. 9, 2009; and “MEMBRANEELECTRODE ASSEMBLY AND FUEL CELL USING THE SAME”, U.S. patentapplication Ser. No.12/384,931,filed Apr. 9, 2009; the disclosures ofthe above-identified applications are incorporated herein by reference.The application is also related to co-pending applications entitled“MEMBRANE ELECTRODE ASSEMBLY AND METHOD FOR MAKING THE SAME”, U.S.patent application Ser No. 12/006,309,filed Dec. 29, 2007 ; “MEMBRANEELECTRODE ASSEMBLY AND METHOD FOR MAKING THE SAME”, U.S. patentapplication Ser. No. 12/006,336, filed Dec. 29, 2007 ; “MEMBRANEELECTRODE ASSEMBLY AND METHOD FOR MAKING THE SAME”, U.S. patentapplication Ser. No. 12/200,338, filed Aug. 28, 2008.

BACKGROUND

1. Technical Field

The disclosure generally relates to membrane electrode assemblies andfuel cell using the same, and particularly, to a membrane electrodeassembly based on carbon nanotubes and a fuel cell using the same.

2. Description of Related Art

Fuel cells can generally be classified into alkaline, solid oxide, andproton exchange membrane fuel cells. The proton exchange membrane fuelcell has received increasingly more attention and has developed rapidlyin recent years. Typically, the proton exchange membrane fuel cellincludes a number of separated fuel cell work units. Each work unitincludes a fuel cell membrane electrode assembly (MEA), flow fieldplates (FFP), current collector plates (CCP), as well as related supportequipments, such as blowers, valves, and pipelines.

Referring to FIG. 12, the MEA 50 generally includes a proton exchangemembrane 51 and two electrodes 54 located adjacent to two oppositesurfaces of the proton exchange membrane 51 according to the prior art.Furthermore, each electrode 54 includes a catalyst layer 52 and adiffusion layer 53. The catalyst layer 52 is sandwiched between thediffusion layer 53 and the proton exchange membrane 51. The protonexchange membrane 51 is typically made of a material selected from thegroup consisting of erfluorosulfonic acid, polystyrene sulfonic acid,polystyrene trifluoroacetic acid, phenol formaldehyde resin acid, andhydrocarbons. The catalyst layer 52 includes catalyst materials andcarriers. The catalyst materials can be metal particles, such asplatinum particles, gold particles, ruthenium particles or combinationsthereof. The carriers are generally carbon particles, such as graphite,carbon black, carbon fiber or carbon nanotubes. The diffusion layer 53is constituted of carbon fiber paper.

However, the carbon fiber paper has the following disadvantages.Firstly, the carbon fibers in the carbon fiber paper are not uniformlydispersed, and therefore, the micropores therein defined by the carbonfibers are not uniform. Thus, such structure prevents the diffusionlayer from uniformly diffusing the gases that are needed for the MEA.Secondly, the carbon fiber paper has high electrical resistance, therebythe travel of electrons between the diffusion layer and the externalelectrical circuit is restricted. As a result, the reaction activity ofthe MEA is reduced.

What is needed, therefore, are a membrane electrode assembly and a fuelcell using the same having improved reaction activity.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present membrane electrode assembly and fuel cellusing the same can be better understood with references to the followingdrawings. The components in the drawings are not necessarily drawn toscale, the emphasis instead being placed upon clearly illustrating theprinciples of the present membrane electrode assembly and fuel cellusing the same.

FIG. 1 is a schematic view of a membrane electrode assembly inaccordance with an embodiment.

FIG. 2 is a Scanning Electron Microscope (SEM) image of a drawn carbonnanotube film.

FIG. 3A is a schematic view of carbon nanotube segments of the drawncarbon nanotube film of FIG. 2 joined end to end.

FIG. 3B shows the drawn carbon nanotube films are situated side-by-sideto increase the area of the carbon nanotube structure.

FIG. 3C shows an SEM image of one embodiment of a carbon nanotube filmstructure including include at least two stacked drawn carbon nanotubefilms.

FIG. 3D is an exploded, isometric view of the carbon nanotube filmstructure of FIG. 3C.

FIG. 3E is an exploded, isometric view of another embodiment a carbonnanotube film structure.

FIG. 4 is a Scanning Electron Microscope (SEM) image of an untwistedcarbon nanotube wire.

FIG. 5 is a Scanning Electron Microscope (SEM) image of a twisted carbonnanotube wire.

FIG. 6 is a Scanning Electron Microscope (SEM) image of a pressed carbonnanotube film with the carbon nanotubes.

FIG. 7 is a Scanning Electron Microscope (SEM) image of a pressed carbonnanotube film with the carbon nanotubes arranged along two or moredirections.

FIG. 8 is a Scanning Electron Microscope (SEM) image of a flocculentcarbon nanotube film.

FIG. 9 is a Scanning Electron Microscope (SEM) image of a drawn carbonnanotube film deposited with platinum.

FIG. 10 is a schematic view of a fuel cell in accordance with anembodiment.

FIG. 11 is a schematic view of a fuel cell in accordance with anotherembodiment.

FIG. 12 is a schematic view of a membrane electrode assembly of theprior art.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate at least one present embodiment of the membrane electrodeassembly and fuel cell using the same, in at least one form, and suchexemplifications are not to be construed as limiting the scope of thedisclosure in any manner.

DETAILED DESCRIPTION

References will now be made to the drawings, in detail, to describeembodiments of the membrane electrode assembly and fuel cell using thesame.

Referring to FIG. 1, a membrane electrode assembly 200 according to oneembodiment is shown. The membrane electrode assembly 200 includes aproton exchange membrane 202, a first electrode 204 and a secondelectrode 206. The proton exchange membrane 202 has two oppositesurfaces, a first surface and a second surface. The first electrode 204is located adjacent to the first surface of the proton exchange membrane202 and the second electrode 206 is located adjacent to the secondsurface of the proton exchange membrane 202. The first electrode 204includes a first diffusion layer 204 a and a first catalyst 204 bdispersed therein and the second electrode 206 includes a seconddiffusion layer 206 a and a second catalyst 206 b dispersed therein.

The first diffusion layer 204 a includes a carbon nanotube structure.The carbon nanotube structure includes a plurality of carbon nanotubesdistributed uniformly therein. A plurality of carbon nanotubes arearranged orderly or disorderly, entangled or arranged along a primarydirection in the carbon nanotube structure. For example, the carbonnanotubes can be entangled with each other, forming a carbon nanotubestructure with disordered arrangement of carbon nanotubes.Alternatively, if the carbon nanotube structure includes orderedarrangement of carbon nanotubes, the carbon nanotubes can be primarilyoriented along the same direction, or along two or more directions. Thecarbon nanotubes in the carbon nanotube structure can be selected from agroup consisting of single-walled carbon nanotubes, double-walled carbonnanotubes, and/or multi-walled carbon nanotubes. The length of thecarbon nanotubes ranges from about 200 to about 900 micrometers in oneembodiment.

The carbon nanotube structure can include at least one carbon nanotubefilm, at least one carbon nanotube wire or combination thereof. Thecarbon nanotubes of the first diffusion layer 204 a can be in thestructure of a carbon nanotube film or carbon nanotube wire. In oneembodiment, the carbon nanotube structure has an overall planarstructure. The carbon nanotube film can be a drawn carbon nanotube film,a pressed carbon nanotube film, or a flocculent carbon nanotube film.The area and the thickness of the carbon nanotube structure areunlimited and could be made according to user's specific needs. Thecarbon nanotube structure can be a free-standing structure, e.g. thecarbon nanotube structure can keep its integrity without the use of asupporter.

In one embodiment, the carbon nanotube structure includes one drawncarbon nanotube film. Referring to FIGS. 2, and 3A, each drawn carbonnanotube film includes a plurality of successively oriented carbonnanotube segments 143 joined end-to-end by van der Waals attractiveforce therebetween. One example of carbon nanotube segments 143 joinedend-to-end when drawing the carbon nanotube film is described in thearticle, “Spinning and processing continuous yarns from 4-inch waferscale super aligned carbon nanotube arrays,”(Adv. Mater. 2006, 18,1505-1510, 2006 Wiley-VCH Verlag GmbH & Co KGaA, Weinheim), incorporatedherein by reference. Each carbon nanotube segment 143 includes aplurality of carbon nanotubes 145 parallel to each other, and combinedby van der Waals attractive force therebetween. The carbon nanotubesegments 143 can vary in width, thickness, uniformity and shape. Thecarbon nanotubes 145 in the drawn carbon nanotube film are alsotypically oriented along a preferred orientation.

The drawn carbon nanotube film 14 can be pulled out from a super-alignedcarbon nanotube array 144 on a substrate. A width and a length of thedrawn carbon nanotube film 14 are dependent on a size of the carbonnanotube array 144. In one embodiment, if the substrate is a 4-inchP-type silicon wafer, the width of the drawn carbon nanotube film 14 isin a range from about 0.5 nanometers to about 10 centimeters, and thethickness of the drawn carbon nanotube film 14 is in a range from about0.5 nanometers to about 100 micrometers. The length of the carbonnanotube film drawn 14 from a 4-inch P-type silicon wafer can be greaterthan 10 meters.

Referring from FIG. 3B through FIG. 3E, the carbon nanotube structureincludes two or more drawn carbon nanotube films 14. The two or moredrawn carbon nanotube films 14 can be situated side-by-side and/orstacked with each other to form a planar carbon nanotube structure.Adjacent drawn carbon nanotube films 14 can be combined with each otherby van der Waals attractive force therebetween. An angle α between thepreferred orientations of the carbon nanotubes 145 in the two adjacentstacked drawn carbon nanotube films 14 is in a range of 0≦α≦90°. Thus,the carbon nanotube structure includes a plurality of micropores definedby the stacked drawn carbon nanotube films 14. The micropores of oneembodiment are distributed in the carbon nanotube structure uniformly.Diameters of the micropores can range from about 1 to about 10micrometers. The micropores can be used to diffuse the gas. It is to beunderstood that there can be some variation in the carbon nanotubestructure.

Further, the carbon nanotube structure can include at least one carbonnanotube wire. A single carbon nanotube wire can be folded, convolutedor otherwise shaped to form the planar carbon nanotube structure.Alternatively the carbon nanotube structure can include a plurality ofcarbon nanotube wires, the carbon nanotube wires can be located side byside, crossed, or weaved together to form the planar carbon nanotubestructure. The carbon nanotube wire can be twisted or untwisted. Theuntwisted carbon nanotube wire is formed by treating the drawn carbonnanotube film with an organic solvent. Specifically, the drawn carbonnanotube film is treated by applying the organic solvent to the drawncarbon nanotube film so as to soak the entire surface of the drawncarbon nanotube film in the organic solvent. After being soaked by theorganic solvent, the adjacent paralleled carbon nanotubes in the drawncarbon nanotube film will be bundled together, due to the surfacetension of the organic solvent when the organic solvent volatilizing,and thus, the drawn carbon nanotube film is shrunk into untwisted carbonnanotube wire. The organic solvent is volatile. Referring to FIG. 4, theuntwisted carbon nanotube wire includes a plurality of carbon nanotubessubstantially oriented along the same direction (e.g., a direction alongthe length of the untwisted carbon nanotube wire). The carbon nanotubesare parallel to the axis of the untwisted carbon nanotube wire. A lengthof the untwisted carbon nanotube wire can be set as desired. A diameterof the untwisted carbon nanotube wire can be in a range from about 0.5nanometers to about 100 micrometers.

The twisted carbon nanotube wire can be formed by twisting a drawncarbon nanotube film by using a mechanical force to turn two ends of thecarbon nanotube film in opposite directions. Referring to FIG. 5, thetwisted carbon nanotube wire includes a plurality of carbon nanotubesoriented around an axial direction of the twisted carbon nanotube wire.The carbon nanotubes are aligned around the axis of the carbon nanotubetwisted wire like a helix.

Referring to FIG. 6 and FIG. 7, the carbon nanotube structure caninclude at least one pressed carbon nanotube film. The pressed carbonnanotube film can be isotropic. The carbon nanotubes in the pressedcarbon nanotube film can be substantially arranged along the samedirection or arranged along two or more directions as shown in FIG. 7.The carbon nanotubes in the pressed carbon nanotube film can rest uponeach other. The adjacent carbon nanotubes are combined and attracted byvan der Waals attractive force, thereby forming a free-standingstructure after being pressed. An angle between a primary alignmentdirection of the carbon nanotubes and a base of the pressed carbonnanotube film can be in a range from about 0 degrees to about 15degrees. The pressed carbon nanotube film can be formed by pressing acarbon nanotube array. The angle is closely related to pressure appliedto the carbon nanotube array. The greater the pressure, the smaller theangle. The carbon nanotubes in the pressed carbon nanotube film can beparallel to the surface of the pressed carbon nanotube film when theangle is 0 degrees. A length and a width of the pressed carbon nanotubefilm can be set as desired. Also, multiple pressed carbon nanotube filmscan be stated upon one another.

Referring to FIG. 8, the carbon nanotube structure may include at leastone flocculent carbon nanotube film. The flocculent carbon nanotube filmis formed of a plurality of carbon nanotubes entangled with each other.The length of the carbon nanotubes in the flocculent carbon nanotubefilm can be larger than 10 micrometers. The adjacent carbon nanotubesare combined and entangled by van der Waals attractive forcetherebetween, thereby forming a microporous structure. Further, theflocculent carbon nanotube film is isotropic. The sizes of themicropores can be less than 10 micrometers. The micropores can be usedto diffuse the gas. The length and a width of the flocculent carbonnanotube film is not limited. In one embodiment, the flocculent carbonnanotube film includes a plurality of long, curved, disordered carbonnanotubes entangled with each other.

The carbon nanotube structure can include other materials, such as afiller thus becoming carbon nanotube composite. The filler can becomprised of a material selected from a group consisting of metal,ceramic, glass, carbon fiber and combinations thereof.

The catalyst 204 b, 206 b include metal particles. The metal particlescan be selected from a group consisting of platinum particles, goldparticles, ruthenium particles and combinations thereof. The metalparticles are dispersed on surface of the carbon nanotube of the carbonnanotube structure uniformly. The distribution of the metal particles isless than 0.5 milligram per square centimeter. In one embodiment, themetal particles are platinum.

In one embodiment, the carbon nanotube structure includes a plurality ofstacked drawn carbon nanotube films. The first electrode 204 isfabricated by the following steps of: (a1) providing two or more drawncarbon nanotube films; (b1) forming a layer of catalyst particles oneach drawn carbon nanotube film; (c1) staking the drawn carbon nanotubefilms to form a carbon nanotube composite structure, thereby obtainingthe first electrode 204. In step (b1), the catalyst particles areplatinum and they are formed by sputtering. Referring to FIG. 9, theplatinum particles are dispersed on the surface of the carbon nanotubesof the drawn carbon nanotube film uniformly. Alternatively, the carbonnanotube structure can include a plurality of carbon nanotube wiresweaved together to form the planar carbon nanotube structure. After step(b1), the drawn carbon nanotube film can be rolled or shrunk to form acarbon nanotube wire. A plurality of wires can be weaved to form aplanar carbon nanotube composite structure.

The material of the proton exchange membrane 202 can be selected from agroup consisting of perfluorosulfonic acid, polystyrene sulfonic acid,polystyrene trifluoroacetic acid, phenol-formaldehyde resin acid, andhydrocarbons. In one embodiment, the second electrode 206 has the samestructure with the first electrode 204.

Alternatively, the second electrode 206 can be a double-layer structure(not shown) that includes a diffusion layer and a catalyst layer. Thecatalyst layer is located between the diffusion layer and the protonexchange membrane, and contact with the diffusion layer and the protonexchange membrane. The diffusion layer can be a carbon nanotubestructure or carbon fiber paper. The catalyst layer includes a pluralityof catalyst materials and a plurality of carriers. The catalystmaterials include metal particles. The metal particles can be selectedfrom a group consisting of platinum particles, gold particles, rutheniumparticles and combinations thereof. The carriers include carbonparticles. The carbon particles can be comprised of a material selectedfrom a group consisting of graphite, carbon black, carbon fiber, carbonnanotubes and combinations thereof. The distribution of the metalparticles is less than 0.5 milligram per square centimeter.

The second electrode 206 can be fabricated by the following steps of:(a) providing metal particles and carbon particles, and putting theminto a dispersion solution; (b) adding water and an active surface agentto the dispersion solution to obtain a catalyst slurry; and (c) coatingthe catalyst slurry on the carbon nanotube structure and drying thecatalyst slurry, thereby forming the catalyst layer on the carbonnanotube structure to obtain the first electrode.

Referring to FIG. 10, a fuel cell 20 is further provided according toone embodiment. The fuel cell 20 includes a membrane electrode assembly(MEA) 200, a first flow field plates (FFP) 208 a, a second flow fieldplates (FFP) 208 b, a first current collector plate (CCP) 210 a, asecond current collector plate (CCP) 210 b, as well as first supportequipment 212 a and second support equipment 212 b. The membraneelectrode assembly 200 can be the membrane electrode assembly (MEA) 200provided in one of the previous embodiments.

The FFP 208 a, 208 b is made of metals or conductive carbon materials.The first FFP 208 a is located adjacent to a surface of the firstelectrode 204 facing away from the proton exchange membrane 202. Thesecond FFP 208 b is located adjacent to a surface of the secondelectrode 206 facing away from the proton exchange membrane 202. EachFFP 208 a, 208 b has at least one flow field groove 214. The flow fieldgroove 214 is contacted with the electrodes 204, 206. Thus, the flowfield groove 214 is used to transport the fuel gases, the oxidant gases,and the reaction product (e.g., water).

The CCP 210 a, 210 b is made of conductive materials such as metal. Thefirst CCP 210 a is located adjacent to a surface of the first FFP 208 afacing away from the proton exchange membrane 202. The second CCP 210 bis located adjacent to a surface of the second FFP 208 b facing awayfrom the proton exchange membrane 202. Thus, the CCP 210 a, 210 b isused to collect and conduct the electrons generated by the work processof MEA 200.

Referring to FIG. 11, a fuel cell 20 is further provided accordinganother embodiment. The fuel cell 20 has similar structure to the fuelcell 20 provided in the previous embodiments except that it has no CCPbecause the carbon nanotube structure has excellent conductivity and cancollect and conduct the electrons. The carbon nanotube structure canperform all of the functions of the CCP, thus eliminating the need forthe CCP. This will reduce the materials needed to make the fuel cell 20.In other embodiments (not shown) one CCP will be employed on one side ofthe proton exchange membrane 202, while the carbon nanotube structurewill collect and conduct electrons on the other side.

The related support equipments 212 a, 212 b include blowers, valves, andpipelines. The blower is connected with the FFP 208 a, 208 b viapipelines. The blowers blow the fuel gases and the oxidant gases.

In the working process of the fuel cell 20, oxygen is applied to thefirst electrode 204 and hydrogen is applied to the second electrode 206.In the second electrode 206, after the hydrogen has been applied to thesecond catalyst layer 206 b, a reaction of each hydrogen molecule is asfollows: H₂→2H⁺+2e. The hydrogen ions generated by the above-describedreaction reach the cathode through the proton exchange membrane 202. Atthe same time, the electrons generated by the reaction also arrive atthe first electrode 204 by an external electrical circuit. In the firstelectrode 204, oxygen is also applied to the first catalyst 204 b. Thus,the oxygen reacts with the hydrogen ions and electrons as shown in thefollowing equation: ½O₂+2H⁺+2e→H₂O. In the electrochemical reactionprocess, the electrons generate an electrical current, and as a result,are able to output electrical energy to the load 220.

In one embodiment, the diffusion layer includes the carbon nanotubestructure. The carbon nanotube structure includes a plurality ofmicropores uniformly distributed therein. As such, on one side of MEA200, the hydrogen can be effectively and uniformly diffused in thecarbon nanotube structure. The hydrogen fully contacts with metalparticles in the second electrode 206. Thus, the catalytic reactionactivity of the metal particles with the hydrogen is enhanced. On theother side of the MEA 200, the oxidant gases are also uniformly diffusedin the carbon nanotube structure, thereby fully contacting with themetal particles in the first electrode 204. Thus, the catalytic reactionactivity of the metal particles with the hydrogen ions and electrons isenhanced. Due to the carbon nanotube structure having good conductivity,the electrons needed or generated in the reactions are quickly conductedby the carbon nanotube structure. This presents a more efficientmembrane electrode assembly.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the disclosure. Variations maybe made to the embodiments without departing from the spirit of thedisclosure as claimed. The above-described embodiments illustrate thescope of the disclosure but do not restrict the scope of the disclosure.

It is also to be understood that the above description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A membrane electrode assembly comprising: aproton exchange membrane comprising two surfaces; and two electrodesseparately located, on the two surfaces, wherein at least one of the twoelectrodes comprises a carbon nanotube composite structure, the carbonnanotube composite structure comprises a carbon nanotube structure and acatalyst material dispersed in the carbon nanotube structure; whereinthe carbon nanotube structure comprises at least one drawn carbonnanotube film, the at least one drawn carbon nanotuhe film comprises aplurality of carbon nanotube segments successively oriented along afixed direction, and joined end-to-end by van der Waals attractive forcetherebetween along the fixed direction, wherein each carbon nanotubesegment comprises a plurality of carbon nanotubes parallel to each otherand combined by van der Waals attractive force therebetween, and amajority of the carbon nanotubes of the at least one drawn carbonnanotube film are oriented along the fixed direction.
 2. The membraneelectrode assembly as claimed in claim 1, wherein the carbon nanotubestructure is planar.
 3. The membrane electrode assembly as claimed inclaim 1, wherein the carbon nanotuhe structure further comprises atleast one carbon nanotube wire.
 4. The membrane electrode assembly asclaimed in claim 3, wherein the at least one carbon nanotube wire is anuntwisted carbon nat otube wire comprising a plurality of carbonnanotubes joined end-to-end by van der Waals attractive force, theplurality of carbon nanotubes are parallel to an axis of the untwistedcarbon nanotube wire.
 5. The membrane electrode assembly as claimed inclaim 3, wherein the at least one carbon nanotube wire is a carbonnanotube twisted wire comprising a plurality of carbon nanotubes alignedaround an axis of the carbon nanotube twisted wire in a helix way. 6.The membrane electrode assembly as claimed in claim 1, wherein thecarbon nanotube structure comprises a plurality of microporesdistributed therein, and diameters of the micropores range from about 1to about 10 micrometers.
 7. The membrane electrode assembly as claimedin claim 1, wherein the catalyst material comprises metal particles. 8.The membrane electrode assembly as claimed in claim 7, wherein the metalparticles are selected from a group consisting of platinum particles,gold particles, ruthenium particles and combinations thereof.
 9. A filetcell comprising: a first flow field plate; a second flow field plate; amembrane electrode assembly located between the first flow field plateand the second flow field plate, the membrane electrode assemblycomprising: a proton exchange membrane comprising a first surface and asecond surface opposite to the first surface; a first electrode, locatedon the first surface, comprising a carbon nanotube composite structure,wherein the carbon nanotube composite structure comprises a carbonnanotube structure and catalyst material disposed in the carbon nanotubestructure; and a second electrode, located on the second surface,comprising a carbon nanotube composite structure, wherein the carbonnanotube composite structure comprises a carbon nanotube structure andcatalyst material disposed in the carbon nanotube structure; wherein thecarbon nanotube structure comprises at least one drawn carbon nanotubefilm, the at least one carbon nanotube film comprises a plurality ofcarbon nanotube segments successively oriented along a fixed direction,and joined end-to-end by van der Waals attractive force therebetweenalong the fixed direction, wherein each carbon nanotube segmentcomprises a plurality of carbon nanotubes parallel to each other andcombined by van der Waals attractive force therebetween, and a majorityof the carbon nanotubes of the at least one drawn carbon nanotube filmare oriented along the fixed direction.
 10. The fuel cell as claimed inclaim 9, further comprising a first current collector plate and a secondcurrent collector plate, wherein the first current collector is locatedon a surface of the first flow field plate and is spaced from themembrane electrode assembly, the second current collector is located ona surface of the second flow field plate and is spaced from the membraneelectrode assembly.
 11. The membrane electrode assembly as claimed inclaim 1, wherein the carbon nanotube structure comprises two or morestacked drawn carbon nanotube films, adjacent drawn carbon nanotubefilms are combined with each other by van der Waals attractive forcetherebetween, an angle between the fixed directions of the majority ofthe carbon nanotubes of the two adjacent stacked drawn carbon nanotubefilms is in a range from about 0 degrees to about 90 degrees.
 12. Thefuel cell as claimed as claimed in claim 9, wherein the carbon nanotubestructure comprises two or more stacked drawn carbon nanotube films,adjacent drawn carbon nanotube films are combined with each other by vander Waals attractive force therebetween, an angle between the fixeddirections of the majority of the carbon nanotubes of the two adjacentstacked drawn carbon nanotube films is in a range from about 0 degreesto about 90 degrees.
 13. The membrane electrode assembly as claimed inclaim 1 wherein the at least one drawn carbon nanotube film is pulledout from a super-aligned carbon nanotube array located on a substrate.